This invention relates to outlet gates used on railroad hopper cars and is particularly concerned with a pan gasket for sealing the junction between the bottom wall of a hopper car and an outlet gate. Hopper cars are used to transport granular materials such as grains and plastic pellets. The hopper car body typically has partitions dividing the car into separate compartments. Each compartment has slanted bottom walls extending to and defining an outlet aperture. A separate outlet gate is attached to the underside of the bottom wall. The gate has means for closing off the outlet aperture and selectively openable means for unloading lading, either by gravity or vacuum-assisted methods.
An outlet gate pan gasket is typically located between the outlet gate flange and the flange on the hopper car's bottom wall. The gaskets are intended to assure that no cracks or crevices are present at the outlet gate which might trap granular material. This is important because if material becomes lodged at the outlet gate junction with the bottom wall, there is a potential that the trapped material will subsequently become dislodged and compromise the quality of the next carload.
To prevent this, outlet gate pan gaskets have been used to seal the junction between the hopper bottom wall and outlet gate. All outlet gate pan gaskets are subject to forces of the loaded granular material in the hopper car. Fluent granular material imposes forces similar to the head of a column of liquid. These forces can cause the gasket to deform and permit granules to enter between the gasket and either the outlet gate flange or the mounting flange at the bottom of the car. Such granules can subsequently be dislodged and cause contamination of subsequent loads in the car.
Prior designs of outlet gate pan gaskets have not been entirely successful in achieving the objective of preventing contamination. One such prior art design is shown in cross-section in FIG. 1. The gasket 1 has an internally-facing flange portion 2 that was molded with a hollow chamber 3 throughout its length. This gasket was not sufficiently strong to permit compression of the inner flange 2 in a way to insure consistent loading and consistently maintained loading.